Some of the most severe earthquakes in the United States occurred not on the Pacific
Coast but in the middle of the continent in southeastern Missouri near the town of
New Madrid.
There are many things that were unusual about the New Madrid earthquakes of 1811-1812.
First, their location is a surprise. There were centered at the southeast corner of
Missouri far from the
seismic active zones of the mountain chains on the edges of continents, which are the
boundaries of techtonic plates. Second, their magnitudes were
unusually high; in the range of 8.1-8.3. Third, the pattern was unusual
in that there were three shocks of about the same magnitude separated by weeks in time.
The table
below gives the timings of the three major shocks. There were numerous aftershocks
following
each major shock.

The New Madrid Earthquakes of 1811-1812

Date

Time of Day

Magnitude

December 16, 1811

2 A.M.

8.2

January 23, 1812

8.1

February 7, 1812

3:15 A.M.

8.3

The estimated locations of the epicenters of these earthquakes are shown below:

Several towns, including New Madrid, shown on the above map were destroyed by the quakes.
In Little Prairie fifteen minutes after one aftershock on December 16th water rose to waist
level and the towns people had to walk through this water eight miles to reach high ground.
They went on another twenty six miles over a three day period seeking refuge in New Madrid
only to find it had been destroyed.

In addition to these three major quakes there were inumerable minor ones, following and sometimes preceding the
major ones. One careful observer noted an average of about forty per day over a three month
month period. There was a notably strong quake on January 7 but it was not of a level 8
magnitude.

The magnitudes of the quakes were estimated from the descriptions of their effects.
Some of these effects were:

The perception of the shock, even the ringing of church bells, at great distances
from the quake. The December 16th quake rang church bells in Pennsylvania and in South
Carolina.
The February 7th quake was
said to have been felt strong enough to rattle windows in Montreal, Quebec, over a
thousand
miles away.

The modification of the channel of the Mississippi River.

The rising of some sections of land, the falling of other sections. Six foot falls
were
created in the Mississippi River. At some points there were reports that the Mississippi
ran backwards.

The creation of new ten new lakes, the largest of which was Reelfoot Lake in
northwestern
Tennessee. In other places the land rose and lakes disappeared.

Some islands in the rivers disappeared.

Trees broke loudly from the violent shaking.

The rising of dead trees from river and lake bottoms.

The creation of crevasses in the earth as much as ten feet wide. Sometimes
the crevasses
opened and then closed spurting water and sand into the air.

The creation of water spouts rising as high as fifteen feet into the air.

The liquification of ground and the subsequent sinking of structures.

The toppling of brickwork, particularly chimneys.

People being thrown out of their beds.

This map shows the range over which the effects of the quakes were felt. The dark
red
zone is where the severe shaking was felt. The lighter red is where shaking was felt but
without damage.

There were other things that occurred such as flashes of light, loud noises and smelly gases spreading
over the land. Watery sand spouts were particularly wide spread. The water was warm. They left holes in the ground and
sometimes sand cones where the sand came down. Sometimes chunks of wood or coal as heavy as
20 pounds were blown out of these sand spouts. The map below shows the area in which sand
spouts occurred.

Wild animals were disturbed by the quakes, seeming to lose their fear of humans. Horses
reacted to the quakes by stop moving or proceding as if they were walking on ice.

The major puzzle concerning the New Madrid earthquakes is why they occurred in midcontinent.
The answer seems to be that a break in the North American plate was developing along the
route of what became the Mississippi Valley. A rift valley was developing but the fissure
ended in the region of New Madrid.

(To be continued.)

Sources:

Norma Bagnall, The New Madrid earthquakes of 1811-1812, Columbia, MO:
University of Missouri Press, c1996.

Jay Feldman, When the Mississippi ran backwards : empire, intrigue, murder, and the
New Madrid earthquakes, New York : Free Press, c2005.